Jonathan Stordy – formerly of Diageo – has become Beam's managing director for the UK and Spain with immediate effect, although McKeon will stay with Beam until the end of June.
In a statement, Beam said it recognised McKeon for the contribution he has made to the success of its UK business.
Managing director of Beam Global, Donard Gaynor, said: "During the course of his tenure, Adrian has served the company admirably and with great distinction. We wish him luck in his new venture."
McKeon will join Cobra in August and founder Lord Karan Bilimoria will move to the role of executive chairman. Bilimoria said: "I have always said that a chief executive should be an all-rounder, and I know that Adrian will bring a range of abilities to Cobra Beer."